A tulku (Tibetan: སྤྲུལ་སྐུ, Wylie: sprul sku, ZYPY: Zhügu, also tülku, trulku) is a custodian of a specific lineage of teachings in Tibetan Buddhism who is given empowerments and trained from a young age by students of his predecessor.

The word སྤྲུལ or 'sprul' (Modern Lhasa Tibetan [ʈʉl]) was a verb in Old Tibetan literature and was used to describe the བཙན་པོ་ btsanpo ('emperor'/天子) taking a human form on earth. So the 'sprul' idea of taking a corporeal form is a local religious idea alien to Indian Buddhism and other forms of Buddhism (e.g. Theravadin or Zen). Over time, indigenous religious ideas became assimilated by the new Buddhism; e.g. 'sprul' became part of a compound noun, སྤྲུལ་སྐུ་'sprul.sku' ("incarnation body" or 'tülku', and 'btsan', the term for the imperial ruler of the Tibetan Empire, became a kind of mountain deity). The term tülku became associated with the translation of the Sanskrit philosophical term nirmanakaya. According to the philosophical system of trikaya or three bodies of Buddha, nirmanakaya is the Buddha's "body" in the sense of the bodymind (Sanskrit: nāmarūpa). Thus, the person of Siddhartha Gautama, the historical Buddha, is an example of nirmanakaya. In the context of Tibetan Buddhism, tülku is used to refer to the corporeal existence of enlightened Buddhist masters in general.

In addition to Tibetans and related peoples, Tibetan Buddhism is a traditional religion of the Mongols and their relatives. The Mongolian word for a tulku is qubilγan, though such persons may also be called by the honorific title qutuγtu (Tib: 'phags-pa and Skt: ārya or 'superior', not to be confused with the historic figure, 'Phags-pa Lama or the script attributed to him, 'Phags-pa script), or hutagt in the standard Khalkha dialect. According to the Light of Fearless Indestructible Wisdom by Khenpo Tsewang Dongyal: designates one who is "noble" (or "selfless" according to Buddha's usage) and used in Buddhist texts to denote a highly achieved being who has attained the first bhumi, a level of attainment which is truly egoless, or higher.

The Chinese word for tulku is huófó (活佛), which literally means "living Buddha" and is sometimes used to mean tulku.

When an old tulku dies, a committee of senior lamas convenes to find the young reincarnation. The group may employ a number of methods in their search. First, they will probably look for a letter left behind by the departed tulku indicating where he intends to be born again. They will ask the close friends of the departed to recall everything he said during his last days, in case he may have given hints. Often, an oracle is consulted. Sometimes a prominent lama has a dream that reveals details of the child's house, parents, or of geographical features near his home. Sometimes heaven presents a sign, perhaps a rainbow, leading the search party to the child.[2]

He is brought up inside a monastery, under the direction of a head tutor and a number of other teachers or servants. He must study hard and adhere to a strict regimen. He has few if any toys or playmates, and is rarely allowed outside. Early on, he learns to receive important visitors, take part in complicated rituals, and give blessings to followers and pilgrims. Sometimes one or both parents are allowed to live near the young tulku. Older brothers are sometimes inducted into the monastery as monk-companions for the holy child. Yet his elderly tutors are the most influential people in his life, and they become his de facto parents.[3]

The academic atmosphere is balanced by unconditional love:

Countering the bleak academic regimen is an atmosphere of overwhelming, unconditional love. During the tulku's every waking moment, monks, family members, and awed, adoring visitors, shower the youth with love.

If you visit a child tulku, you will probably notice that his quarters are pervaded by a wonderful glow. Everyone beams at the tulku. The tulku beams back. If he asks for something, he is given it immediately, and if he errs, he is corrected just as immediately. Western visitors to the young 14th Dalai Lama commented on “the extraordinary steadiness of his gaze.” Even when quite young, the boys have remarkable poise; they sit calmly without fidgeting, even through ceremonies that may last all day.[4]

The tulku system of preserving Dharma lineages did not operate in India. The first tulku line of Tibet is the Karmapas. After the first Karmapa died in 1193, a lama had recurrent visions of a particular child as his rebirth. This child (born ca. 1205) was recognized as the second Karmapa, thus beginning the Tibetan tulku tradition.[citation needed]

And now, I personally think that to hold that culture, institutionalized Tulku. That culture is dying; it’s not going to work anymore. And even if it… And if it doesn’t work, I think it’s almost for the better because this tulku, it’s going to… If the Tibetans are not careful, this Tulku system is going to ruin Buddhism. At the end of the day Buddhism is more important [than] Tulku system, who cares about Tulku... [and] what happens to them.[6]

^Khenpo Ngawang Pelzang. A Guide to the Words of My Perfect Teacher. Boston: Shambhala. 2004. ISBN 978-1-59030-073-2. "This form of transference is practiced by beginners on the path of accumulating who have received empowerment and respected the samayas, have a good understanding of the view, and have practiced the generation phase as the path but have not mastered it. Although they lack the necessary confidence to be liberated in the clear light at the moment of death or in the intermediate state of absolute reality, by taking refuge and praying to their teacher in the intermediate state they can close the way to an unfavorable womb and choose a favorable rebirth. Propelled by compassion and bodhichitta, they depart to a pure buddhafield or, failing that, take birth as a tulku born to parents who practice the Dharma. In that next life they will be liberated."